1. Field of the Invention
The present invention relates to multilayer films. More particularly, the invention pertains to coextruded or laminated films having at least one layer of a halopolymer such as poly(chlorotrifluoro ethylene) (PCTFE), at least one layer of a naphthalene containing polymer such as poly(ethylene naphthalate) (PEN), poly(butylene naphthalate) (PBN), and the like including copolymers and blends thereof, and an intermediate adhesive layer.
2. Description of the Related Art
It is well known in the art to produce multilayer polymer films. For example, see U.S. Pat. Nos. 4,677,017 and 5,139,878, which are hereby incorporated by reference. Such show a multilayer film having a thermoplastic fluoropolymer layer and a thermoplastic polymeric layer attached to the thermoplastic fluoropolymer layer, preferably via an intermediate adhesive layer. These films may be made by well known lamination and/or coextrusion techniques. Lamination methods are also known from U.S. Pat. No. 3,355,347 which is incorporated herein by reference. These multilayer films may be symmetrical or asymmetrical, oriented or unoriented. The orientation or stretching of films is also known in the art as shown by U.S. Pat. Nos. 4,677,017 and 5,139,878.
It has been a problem in the art to produce a transparent or translucent films with sufficient clarity to protect light sensitive materials, especially in outdoor applications, since many such materials have a tendency to degrade. Films which are used to protect food, medicines, paints, adhesives, biomaterials, chemicals, etc., require properties such as good thermal and environmental stability, excellent moisture barrier, UV blocking characteristics, and transparency in visible light wavelengths.
Fluoropolymers have been commonly used in outdoor applications due to their extraordinary UV light stability. Such include poly(tetrafluoroethylene-co-ethylene) (ETFE), and tetrafluoroethylene-hexafluoropropylene copolymers (FEP), etc. Since they are transparent in most UV light wavelength regions (i.e., 200 nm-400 nm), they cannot adequately protect the contents underneath although they are extremely stable.
It is also known in the art to use UV absorbers, e.g., benzotriazole derivatives, hindered amines, hydroxybenzophenone derivatives, etc. to impart UV blocking characteristics. However, these UV absorbers are low molecular weight materials (i.e., molecular weight less than 1,000) which are either sanctioned for direct food contact and pharmaceutical applications or restricted to be used at a low concentrations due to the tendency of these absorbers to migrate to the film surface. They are also not very thermally stable. As a result their UV blocking characteristics are ineffective and limited, especially in a thin film. Except for fluoropolymers, most moisture barrier polymers are not UV stable. For example, poly(vinylidene chloride) (PVdC) turns yellow and embrittles under UV light. Other moisture barrier polymers, such as polyolefins, also need UV stabilization to prolong their shelf life under severe UV environments.
It has been known that poly(ethylene naphthalate) (PEN) has excellent UV blocking characteristics. However, because of its extremely slow crystallization rate, PEN is very brittle and its cast film cannot be used alone as a free standing film. Therefore, only oriented PEN film is commercially available. However due to its already highly oriented structure, it cannot be thermoformed into blister packages for pharmaceutical applications. PEN polymer also lacks moisture barrier as compared to PVdC or PCTFE; and as a result, it is rarely used as a moisture packaging material. PEN polymer is known to lack chemical resistance and it is seldom used in an outdoor application by itself Poly(chlorotrifluoro ethylene) (PCTFE) polymer has excellent moisture barrier and non-stick property despite its lack of UV blocking characteristics.
The invention provides a multilayer film which comprises at least one halopolymer layer, attached to at least one naphthalene containing polymer layer by an intermediate adhesive layer.
The invention also provides a method of producing a multilayer film which comprises coextruding at least one layer of a halopolymer, and at least one naphthalene containing polymer layer attached to the halopolymer layer via an intermediate adhesive layer.
The invention further provides a method of producing a multilayer film which comprises laminating at least one layer of a halopolymer to a layer of a naphthalene containing polymer by an intermediate adhesive layer.
The invention achieves a multilayer film with enhanced UV blocking characteristics, a non-stick surface as well as moisture protection. The combination of a naphthalene containing film and a halopolymer film provides a multilayer film that blocks light in UV wavelength (i.e., 200-400 nm), is transparent in the visible light range (i.e., 400-800 nm), is stable in an outdoor environment, and has excellent moisture barrier properties and chemical resistance.
It would be desirable to produce a multilayer film which is a combination of a PEN polymer layer and a PCTFE layer not only blocks light in the UV wavelength while maintaining transparency in the visible light region, but is also stable environmentally due to the excellent moisture protection and chemical resistance provided by PCTFE. It would also be desirable to produce a multilayer film by combining PEN and PCTFE films through an intermediate adhesive polymer to alleviate the brittle nature of cast PEN film and allow the film to have a practical use.